This invention relates to an automatic electronic ice-making control system for automatic ice-making machines.
Heretofore, in automatic ice-making machines of the type wherein an evaporator of the freezing system is arranged in the ice-making compartment for ice freezing, a number of detecting methods and equipments utilizing, for example, semiconductor temperature sensitive elements have been proposed for detecting the ice made state by measuring variations in temperature in the ice-making chamber with start of defrosting.
However, merely monitoring temperature variations is not sufficient to provide the desired results of this invention; i.e. making substantially the same quantity of ice by the ice-making machine independently of the season during which the ice-making machine is used. In such case, cooling time which is a function of ambient temperature conditions, cannot be ignored. For example, when the outdoor temperature goes down during the Winter, with increase of the cooling efficiency, the time it takes before a temperature sensitive element responds to the temperature actuating point at which a control circuit is to be operated, is relatively short so that the quantity of ice produced in the ice-making chamber during the ice-making cycle is decreased. On the other hand, when the outdoor temperature rises, as it does during the summer, with decrease of the cooling efficiency, the time it takes before the temperature sensitive element senses the temperature actuating point is longer so that the quantity of ice produced in the ice-making chamber is increased because of extended refrigeration which may cause cracks to be formed, lowering ice-making capacity.
It will be apparent therefore that the cooling efficiency of and the quantity of ice made by the ice-making machine is related to ambient temperature conditions; i.e. high efficiency in the Winter and thus less ice formation and lower efficiency in the summer and thus greater ice formation.
Ice-making machines have a freezing compartment, referred to herein as an ice-making chamber, such compartment and heat removing surface, on which a tray or trays for water to be frozen into ice cubes is supported, being illustrated, for example, in U.S. Pat. No. 3,283,526. The heat removing surface which in part forms the ice-making chamber is exposed to the atmosphere and is thus affected by atmospheric ambient temperature conditions. Since the heat removing surface or plate is provided with the temperature sensitive element the latter will therefore also be affected by ambient temperature changes to which the plate is exposed.
To ensure making a substantially uniform quantity of ice by the ice-making machine, independent of atmospheric ambient temperature changes, we provide in accordance with the invention in an ice forming system for ice-making machines having an ice-making chamber, an electronic control circuit for making uniform quantities of ice irrespective of atmospheric ambient temperature changes and comprising a voltage source, a differential amplifier supplied by the voltage source and having as its output a voltage tapped from the junction of series connected first and second temperature responsive elements, the free ends of which are connected to the voltage source, one only of the temperature responsive elements being within the ice-making chamber for detecting temperature changes therein, the other temperature responsive element being exposed to the atmosphere and being sensitive therefore to atmospheric temperature changes, both temperature responsive elements translating temperature changes into impedance changes, the impedance change of the second temperature responsive element with ambient temperature changes being effective to modify the temperature at which the first temperature responsive element is effective to provide a predetermined input voltage of sufficient magnitude to cause conduction of the differential amplifier, and by virtue of other components in the ice-forming system, when the differential amplifier becomes conductive, ice formation is terminated.